There have been devised and embodied hearing aids that moderate hearing impairment by amplifying and outputting collected sound. In order to support user's preferences and use conditions, such hearing aids are various in forms, such as a Behind-the-Ear (BTE) type and a Completely-in-Canal (CIC) type, as disclosed, for example, in Japanese Patent Application Laid-Open No. 7-162997. Any of these hearing aids are driven by an internal battery or a rechargeable battery, and therefore no longer work when supply of power is unexpectedly stopped depending on frequency or duration of use, which is a nagging problem in these hearing aids.
These hearing aids driven by such an internal battery prevent the unexpected stop of power supply by providing an advance notice of battery replacement time or charging time. Such battery replacement work or charging work is, however, very troublesome for the hearing aids used on a daily basis.
The present invention has therefore been proposed in view of the foregoing circumstance, and an object thereof is to provide a hearing aid that reliably supplies power when used without requiring troublesome work such as battery replacement work and charging work.